1. Field of the Invention
The present invention relates to a fluorescence qualitative analytical apparatus and method of analyzing elements contained in a sample and, more particularly, to an efficient method and apparatus for measuring both light and heavy elements in a sample, while avoiding any false signals that can be generated from an X-ray target.
2. Description of Related Art
The ability to analyze the constituent elements, for example, of both light and heavy metal elements in a sample, is valuable in industries and laboratories.
Since technicians sometimes deal with samples containing unknown elements of both a relatively small atomic number, such as Na, Mg, Al, Si, P, S, and Cl, having atomic number of 11, 12, 13, 14, 15, 16, and 17, respectively, and also of elements having relatively larger atomic numbers, for example, Sr, Y, Zr, Nb, Mo, Pd, Ag, In, Sn, Sb, W, Pt, Au, and Pb, having atomic numbers of 38, 39, 40, 41, 42, 46, 47, 49, 50, 51, 74, 78, 79, and 82, respectively, difficulties frequently occur in achieving accuracy in measuring each of the elements that are the constituent parts of the sample.
X-ray analyzers have been developed that generate a stream of electrons of high energy to contact a target which, in turn, emits primary X-rays. The primary X-rays, in turn, will contact a sample to generate fluorescent X-rays which are subsequently measured to determine the elements contained in the sample. The primary X-rays, however, can also be scattered by contacting the sample and can have nearly the same energies as the applied primary X-rays.
In addition, the target material of the X-ray target can also generate characteristic X-rays represented by that specific target material. For example, referring to FIG. 8, an intensity versus X-ray energy curve is disclosed for a target material containing rhodium (Rh), with the target producing a continuous band of X-rays, including an Rh-L X-ray which is characteristic of the X-rays of rhodium. The applied voltage in this condition is 15 kV.
FIG. 9 discloses another graph of a target containing rhodium, subject to an X-ray tube voltage of 50 kV. In FIG. 9, the continuous X-rays produced are shown along with the characteristic X-rays of rhodium, including an Rh-L ray, an Rh-K .alpha., and an Rh-K .sym. ray.
The target can have a characteristic element which will generate its own energy spectrum which can also be received by the detectors attempting to measure the fluorescent X-rays from the sample. For example, if the target contains rhodium (Rh), a measurement output can have the characteristic shown in FIG. 4, wherein the sample disclosing aluminum and copper, could mistakenly be judged to include rhodium as a component. The operator would not know whether the sample contains rhodium or whether this was a characteristic of the target which was perceived in the analysis of the X-rays coming apparently from fluorescent X-rays from the sample. As a result, it can become difficult to carry out a highly accurate quantitative analysis by a technician. The prior art is accordingly seeking an economical method and apparatus to avoid such problems.